Re: [nemo] WG Last Call on draft-ietf-nemo-terminology

[Chan-Wah Ng <[e-mail]>]

On Fri, 2005-11-18 at 10:51 +0900, Romain KUNTZ wrote:
> Hello,
> 
> Thierry Ernst wrote:
> > - A25 (split NEMO)
> 
> I propose the following draft definition:
> 
> A split NEMO occurs when a single mobile subnet connected to multiple 
> Mobile Routers, or multiple mobile subnets interconnected with routers, 
> become two or more independant mobile subnets.

"independent".

Anyway, "multiple mobile subnets interconnected with routers" is not
very accurate and leads to controversy.  Consider

    MR1            MR1
     |              |
  ---+-+---  =>   --+---   MR2
       |                    |
      MR2                 --+--
       |
    ---+----

It fits your definition but does not falls into the normal sense of
split NEMO.

> 
>      |    |             |      |
>     MR1  MR2           MR1    MR2
>      |    |      ->     |      |
>    ----------         -----  -----
> 

The above I agree, the one below needs a bit of further exploration.

> 
>      |             |          |       |
>     MR1  Router   MR2        MR1     MR2
>      |    |  |     |    ->    |       |
>    --------  -------        -----   -----
> 

With a router, presumably a LFR, in between, the two links are separate
subnets.   So, MR1 and MR2 are handling different prefixes.  When the
two links goes separate way, what would happens is that the LFR would no
longer function as a router, since it loses its at least one of its link
for forwarding.

As far as NEMO-BS is concerned, this situation also does not fall into
the normal sense of split-NEMO problem, because MR1 and MR2 are handling
different prefixes, even when they split, there is no ambiguity in the
HA(s) on who to forward a packet destined for one of the MNPs to.

Unless the router in the figure is not a router but a bridge/switch/...,
a layer 2 device.  Which should not reflected, and thus reducing this
case to be equivalent to the first diagram you draw, from a layer 3
perspective.


It all depends on what is the motivation for the inclusion of the
split-NEMO definition.  I thought the motivation was to assist in
illustrating the problem of split NEMO as documented in
draft-ietf-nemo-multihoming-issues.  If this is indeed the case, then
the definition of split-NEMO should define cases only when the problem
of split NEMO occurs.

/rgds
/cwng